Printing plate



Jan. 21, 1936. SWAN r AL 2,028,709

PRINTING PLATE Filed May 26, 1934 Fla)? Haifa INVENTORS l 'TORNEYPatented Jan. 21, 1936 I 2,028,709 PRINTING PLATE Hylton Swan, UpperMontclair, and Sigfrled Higgins, Verona, N. J., assignors to BakeliteCorporation, New York, N. Y., a corporation of Delaware Application May26, 1934, Serial No. 727,722

16 Claims. 01. 41-25) This invention relates to a printing plate andmethod of preparing same.

The relief printing trade at the present time greatly desires a printingplate which is of general application, that is, one which may be usedwith smooth or roughened paper and which is applicable either tofiat-bed or cylindrical types of presses. In an effort to provide such aplate, the rubber plates have found favor but the rubher printingsurfaces are subject to attack by the oils which are in the common inks.In order to prevent the deterioration of the printing surface ofthe-plate, it has been proposed to make plates with either asyntheticresin face or 5 a metal face. A difliculty with a plate faced withsynthetic resin, however, is that the resin sets to a hard brittlecondition so that it must be molded either fiat or curved for aparticular type of press. A difflculty with the metal faced plates isthat they cannot be used for a high grade printing job on rough finishedor antique papers. i 1

Among the objects and features of the present invention is a plate whichcanbe made easily and quickly from materials-readily obtainable in .theopen market and which, when prepared, may be used either on a fiat-bedpress or a rotary cylinder press. By virtue of its resiliency our platehas the definite advantage of materially 80 reducing the time requiredin accurately setting up the plate on the printing press, technicallyknown as make-ready. The printing surface of the plate is extremelytough and wear resist ant, not attacked by oils'and of surprising re- 85sistance to wear and deterioration both in use and in storage before andaft r use. The printing surface takes ink very well from inking rollersor other inking devices and gives it up very readily to the materialupon which the printing 40 is'being done.

The printing surface faithfully reproduces the smallest hair lines anddots on the matrix as well as the largest printing areas without the useof extremely high forming pressures which 45 may damage the matrixsurface, for instance with damp regenerated cellulose a-molding pressurein the neighborhood of 1000 pounds per square inch may be used whereaswith metal faces pressure in the neighborhood of 7000 50 pounds persquare inch and upwards are usually found necessary in commercialpractice. lFurthermore, the plate is resilient so that it may be usedtoprint on either smooth or rough paper.

. Moreover, the printing surface does not-stick to -i,

55 the surface of the synthetic resin matrices which are highly,desirable for use in forming the plate due to their strength, lightweight, durability and fidelity in reproducing the original type orother printing areas.

Other objects and features of the invention will 5 be pointed out in theclaims and will be understood from the following part of thespecification wherein one of the preferred forms of the invention isdisclosed, together with the drawing illustrating a plate and matrix. 1

We have discovered that a plate comprising a rubber body and a printingface comprising a substantially non-thermoplastic unified cellulosematerial for example regenerated cellulose with or without modifyingagents, plasticizers, for in- 15 stance glycerine, waterproofing agents,waxes, etc., for instance the material known on the market asCellophane, has the desirable characteristics which adapt it for almostuniversal use.

The regenerated cellulose is extremely tough 20 and wear resistant andwe have found that it has suflicient strength so that fine lines andsmall dots do not mushroom or spread when printing pressure is appliedyet, on the other hand, when print satisfactorily on rough paper. Inthin sheets, theregenerated cellulose can rather easily be forced toconform to and accurately reproduce the finest detail in a matrix. Thesheets of regenerated cellulose which we use may for example be from.001 to .035 of an inch in thickness. They may also be roughened on oneside, for instance by sand-blasting, to assist the bonding of thesurface to the rubber body. a The rubber body should have sufiicientyield to permit the plate to be used on rough paper but should not beextremely soft, particularly where the rubber body is thick, else theplate will not be solid enough to resist pull or movement in planesparallel to the surface, for accurate register for instance in colorwork. This lateral displacement is particularly noticeable on rotarypresses where, if the plate is too yield- -able,' there is a tendencyfor the printing surface of the plate to shift laterally with relationto the base at the timethat the leading edge of the plate meets .theimpact-of the impression cylinder. Thus aplatewhich has-a relativelybodyithere isless of the elastic yieldable' rubber .to permit-theaplateto yield. on-roughpaper and *there less tendency for the printingsurface to shift laterally with regard to the base. In the case where athick rubber body is used, it is preferably of harder rubber sumcientlyyieldable to permit of some compression when printing on rough paper buthard enough to resist lateral displacement of the printing surface. Forrelatively thin rubber bodies, for example where the rubber is from .125to .150 of an inch in thickness, the body may test between 50 anddurometer test and for a relatively thick rubber body, for example wherethe rubber is from .180 to .250 of an inch in thickness the body maytest between 60 and '75 on the durometer. The proper amount of yield maybe obtained by regulating the amount of vulcanizing agent accelerators,etc., incorporated with the rubber or by incorporating fillers, forinstance zinc oxide, carbon, barium sulphate, asbestos, etc. Thepreferred plate has a body of rubber including one or more sheets ofabsorbent paper or similar material, for instance rubber-impregnatedblotting paper or cork which is readily compressible but has relativelygreat resistance to stretch or movement in a plane parallel to the planeof the printing surface.

If desired, a metallic foundation plate or sheet may be fastened to therear face of the rubber body to assist in holding the plate on thepress. The rubber or rubber-filler composition may thus be.of athickness sufilcient to give a plate of the desired cross section or itmay be thinner to allow for the thickness of the metal or other similarsheet.

An illustrative method of making the plate will now be described, itbeing understood that the description is by way of example only and thatvariations thereof may be made as desired.

A sheet of rubber either with or without filler or embedded fibrousmaterial is first procured. This sheet should contain sufiicientvulcanizing or curing agent to produce the required stiffness uponheating.

The rubber sheet is coated with an adhesive which adheres to both therubber and the regenerated cellulose for example an acid degeneratedrubber in a solvent solution. A general example of a suitable adhesiveis an emulsion or dispersion comprising rubber and a. rubber solventwith ingredients which render tacky the surface of the regeneratedcellulose. Thus one part of the adhesive may comprise an aqueousdispersion of rubber which may for example be reclaimed rubber or rubberlatex, rosin and lime or calcium resinate. instance gasoline or benzolmay be included also. Another part of the adhesive may comprise anaqueous dispersion of rubber, a water soluble adhesive, for example gumarabic or gelatin, 2. peptizing agent, for example, triethanol amine orglycerol and a water soluble. solvent for cellulosic materials forinstance ethyl lactate. The dispersion or emulsion of these .ingredientsmay be used to coat the adjoining surfaces of the rubber and regeneratedcellulose or a sheet of fibrous material, for example paper, blottingpaper or cloth may be coated or impregnated with this adhesive and usedas an intermediate bond between the rubbe and regenerated cellulose. Thesurface of the regenerated cellulose sheet may be coated if desired.

After coating the surface or surfaces to be Joined, with the aboveadhesive or other suitable material, and preferably after waiting untilthe adhesive has a tacky surface, the sheets are assembled and pressedtogether to form a unitary A solvent for the rubber, for

composite sheet. If a metallic foundation plate is used, the adjoiningsurfaces of the metal and rubber or an intermediate cementing sheet may'be coated or impregnated with a suitable metal-. rubber adhesive forinstance with the first mentioned part of the composite adhesive, namelythe rubber dispersion, rosin and lime or calcium resinate, and gasolineor benzol; brought together under pressure. Where the metallic sheet isused, it may be cemented to the rubber before, or after or during thetime that the rubber is cemented to the regenerated cellulose. A stackof the assembled sheets may be held under pressure until the cement hasthoroughly set. If desired, however, the composite sheets may be moldeddirectly after assembly but if wet adhesive is used the press should bevented to allow the escape of the volatile ingredients of the adhesive.

Having made the plate blank, it may be formed into a printing plate inthe following manner. The matrix used is preferably of a heat hardenedsynthetic resin, for instance a phenol formaldehyde condensation productwhich is unaffected by temperatures suitable for the vulcanization ofthe rubber and which does not adhere to the regenerated cellulose. Thesurface of the regenerated cellulose may be moistened slightly with adamp cloth or steam to enable it to stretch more easily. The compositeblank is laid in a press, preferably heated, with the regeneratedcellulose face against the matrix and is subjected to the heat andpressure until the printing surfaces have been formed on the face andpreferably until the rubber has reached the desired state of hardness.It is possible to reand then move the plate from the press before therubber has vulcanized sufiiciently to give the desired hardness and thencontinue the heating in an oven but this is not recommended as the platemay be damaged by such removal. The molding of the printing facepreferably takes place in a semi-positive mold so that there is somecheck offeredto the side fiow of the plastic material which gives aplate with a substantially uniform density and definition at the cornersand edges. v

As the rubber softens under the heat it is pressed toward the matrixforcing the regenerated cellulose surfacing to conform to and thus fill,and reproduce the reverse of, the matrix surface. As the rubber hardensit holds the regenerated cellulose surface film in the positions givenit by the matrix face and upon removal from the mold the plate has atough printing surface which is smooth and relatively hard yetsufficiently yieldable to print on rough paper. The surface. does notscratch easily as does a surface of a metal soft enough to be formed bya corresponding pressure; nor do the small printing areas, for instancethe fine dots on photographic screen reproduced printing areas, spreador mushroom under repeated impacts of the inking rollers or impressioncylinder as would the soft rubber without the regenerated cellulosefacing.

A preferred form of the invention hasfbeen described but it is notintended to exclude modifications thereof. Under proper conditions othertypes of ink resistant surface sheets may be used such, for instance, aspaper treated with zinc chloride or by excessive hydration, as well asbodies of synthetic rubbery products now on the market such, forinstance, as the hydrochlois sold as Duprene, vulcanized sulphurhydrocarbon products one form of which is known as Thiocold, factis, ora rubbery fatty oil-phenolicmethylene product. The oxidized fatty oils,for instance oxidized linseed oil, may be used in part as a modifyingagent as may other modifiers. It is therefore recognized that there aremany variations of the invention and it is desired that the invention beconstrued as broadly as the,

5. A printing plate comprising a facing of unified cellulose and ayieldable body.

'6. A printing plate comprising a facing of non-thermoplastic unifiedcellulose and a yieldable body;

7. A printing plate comprising a facing of unified cellulose and ayieldable body having a durometer reading from substantially 50 tosubstantially 75.

8. A printing plate comprising a facing of unified cellulose, ayieldable body and a stretch resisting layer.

9. A printing plate comprising a facing of unified cellulose, ayieldable body and an interior stretch resisting layer.

10. A printing plate comprising a facing of unified cellulose, ayieldable body and an interior fibrous stretch resisting layer.

11. Method of producing a printing plate comprising forming acompositesheet-having a facing of unified cellulose and a body including rubber,laying the composite sheet in molding position with the unifiedcellulose toward a. matrix and subjecting the assembled parts topressure to mold a printing surface on the unified cellulose from thematrix.

12. Method of producing a printing plate comprising forming a compositesheet having a facing of unified cellulose and a body including rubberand a vulcanizing agent, laying the composite sheet in molding positionwith the unified cellulose toward a matrix,subjecting the assembledparts to pressure to mold a printing surface on the unifiedcellulosefrom the matrix and vulcanizing the rubber.

'13. Method of producing the printing plate comprising forming acomposite sheet having a facing of unified cellulose and a bodyincluding rubber and a vulcanizing agent, laying the composite sheet inmolding position with the unified cellulose toward a matrix, andsubjecting the assembled parts to heat and pressure to mold a printingsurface on the unified cellulose from the matrix and vulcanizing therubber to the desired stiffness.

14. Method of producing the printing plate comprising forming acomposite sheet having a facing of unified cellulose and a bodyincluding rubber and a vulcanizing agent, laying the composite sheet inmolding position with theunified cellulose toward a matrix, subjectingthe assembled parts to pressure to mold a printing surface on theunified cellulose from the matrix and vulcanizing the rubber to adurometer reading from substantially 50 to substantially '75.

'15. A printing plate comprising a facing of unified cellulose, ayieldable body and a backing plate.

16. A printing plate comprising. a facing of unified cellulose, ayieldable body and a thin 4 backing plate, adapted to be curved wherebythe plate may be used either fiat or .curved.

HYLTON SWAN. SIGFRIED HIGGINS.

